A battery cell employs positive electrode, a negative electrode and an electrolyte, sometimes configured as alternating electrode and electrolyte layers. Each electrode may include a current collection substrate and one or more electrochemically active layers. Among the considerations for the current collector design are the following: (a) high electrically conductivity; (b) resistance to corrosion by the electrolyte used; (c) resistance to electrochemical reactions so as not to be consumed too quickly; (d) mechanical strength and flexibility allowing it withstand manufacturing operations (e.g., pasting and rolling); (e) low cost, including material cost and manufacturing; and (f) a surface structure providing good physical contact, or “connectivity,” to the electrochemically active layers (e.g., the material should not form a passivating film so as to prevent the good physical contact and should adhere well to the electrochemically active layers). It is not critical that any one or more of these features be met. For example, a current collector may be outstanding in one or more categories and yet be sub-standard in others. Thus, a material having disadvantages in one aspect may still be used if the disadvantages may be overcome by the overall battery design.
Lead-acid and cadmium-nickel batteries are used widely. Although the lead-acid and cadmium-nickel batteries contain heavy metals and toxic substances such as lead and cadmium, they have stable properties, reliable application and high performance to price ratio. Thus they have been the predominant types of secondary batteries and are used in communication, electric power, automobiles, trains, aviation and aerospace industries, UPS power supplies, household electric appliances, motor tools, motor toys, etc.
A zinc-nickel battery has excellent properties, such as relatively higher over-potential of hydrogen evolution, good reversibility, high energy density, high average voltage (1.65 V), and relatively homogeneous anode dissolution. Even more important, zinc metal is environment-friendly as the use of which does not cause pollution to the environment. Yet zinc-nickel secondary batteries have not been widely commercialized. Zinc metal is amphoteric, very active, and dissolves in both acid and base while producing hydrogen. A zinc metal current collector in an alkaline electrolyte may deform, corrode and deactivate. During charging of a rechargeable nickel-zinc battery, zinc dendritic crystals may generate and grow, causing short circuits when they penetrate separators between the positive and negative electrodes. Thus current collection substrate design has avoided the use of zinc metal as the current collection substrate.
Common materials currently used for zinc negative electrode current collectors include copper and brass. The copper or brass may be punched strips, meshes, foams and the like. The electrodes are formed by adhering an active substance containing zinc element, such as ZnO, Zn or calcium zincate, to one side or both sides of the copper or brass. The contact of the zinc active material with these substrates may accelerate zinc corrosion by promoting hydrogen evolution. This zinc corrosion causes “gas swelling,” creepage and leakage, capacity fading, short cycle lifetime, unsteadiness and unreliability of the zinc-nickel battery.
It is observed that as nickel zinc batteries discharge and recharge over many cycles, the battery capacity reduces. For many applications, a battery is considered dead if the battery capacity after a full recharge is less than 80% of the rated capacity. It is desirable to complete a high number of cycles before a battery dies and avoid the disadvantages of zinc corrosion with a current collector design that meets the design and manufacturing considerations.